Normally, light waves vibrate in a large number of planes about the axis of a light beam. If the waves vibrate in one plane only, the light is said to be plane polarized. Several useful optical systems can be implemented using polarized light. For example, in the manufacture of electro-optical devices such as liquid crystal display screens, crossed polarizers are used in conjunction with an addressable liquid crystal interlayer to provide the basis for image formation. In the field of photography, polarizing filters have been used to reduce the glare and the brightness of specular reflection. Polarizing filters, circular polarizers or other optical components have also been used for glare reduction in display device screens.
Linear light polarizing films, in general, owe their properties of selectively passing radiation vibrating along a given electromagnetic radiation vector, and absorbing electromagnetic radiation vibrating along a second given electromagnetic radiation vector, to the anisotropic character of the transmitting film medium. Dichroic polarizers are absorptive, linear polarizers having a vectoral anisotropy in the absorption of incident light. The term “dichroism” is used herein as meaning the property of differential absorption and transmission of the components of an incident beam of light depending on the polarization direction of the incident light. Generally, a dichroic polarizer will transmit radiant energy polarized along one electromagnetic vector and absorb energy polarized along a perpendicular electromagnetic vector. A beam of incident light, on entering a dichroic polarizer, encounters two different absorption coefficients, one low and one high, so that the emergent light vibrates substantially in the direction of low absorption (high transmission).